During development of the nervous system, neuronal growth cones extend through a complex environment to accurately find their proper target area. Among the features of the environment which growth cones encounter are the axons of other, earlier differentiating neurons. Since growth cones are frequently observed in vivo to associate with other axons, we have chosen to focus our research on growth cone-axon interactions. The long term objective of this research is to isolate cell surface molecules which are localised on neuronal processes and which promote neurite extension. A bioassay which measures neurite extension on axons has been developed. This assay will be used to functionally screen monoclonal antibodies which have first been selected because they are localised on the cell surface and are different from known molecules. Monoclonal antibodies will be generated against crude membrane preparations, or against membrane proteins which have been fractionated by biochemical methods. In conjunction with monoclonal antibody generation, the bioassay will be expanded to include other neural tissues, and new bioassays will be developed. To directly identify membrane proteins which support neurite outgrowth, brain membrane proteins will be fractionated by gel electrophoresis and blotted onto nitrocellulose. Neural cells will be cultured on the blots and assessed for neurite outgrowth.